Response to the environment Flashcards
1
Q
What is a bundle of neurones known as?
A
A nerve
2
Q
What 3 main structures make up a neurone?
A
- A cell body that contains the nucleus
- Axon
- Myelin sheath
3
Q
What are the nodes of Ranvier?
A
Uninsulated gaps between Schwann cells
4
Q
What is the myelin sheath made up from?
A
Made up of specialised cells called Schwann cells
5
Q
What is the structure of relay neurones?
A
- Short neurone with axons and highly branched dendrites (no myelin)
6
Q
What is the structure of motor neurones?
A
- A large cell body that lies in the CNS
- Highly branched dendrites
- Myelinated
7
Q
What is the structure of sensory neurones?
A
- A cell body that branches off in the middle
- No dendrites
8
Q
What is the role of receptor cells?
A
To detect changes in the environment/stimuli
9
Q
What is the pathway of an impulse through the nervous system?
A
- Stimulus
- Receptor
- Sensory neurone
- Relay neurone (CNS)
- Motor neurone
- Effector
10
Q
To dilate the pupil what muscles contract and relax?
A
- Radial muscles contract and the circular muscles relax
11
Q
To constrict the pupil what muscles contract and relax?
A
Circular muscles contract and radial muscles relax
12
Q
What is the resting potential in mV?
A
-70 mV
13
Q
How is resting potential established?
A
- The sodium-potassium pump actively transport 3Na+ out of the cell and 2K+ into the cell
- This establishes an electrochemical gradient making the cell negative
14
Q
Name the stages in generating an action potential
A
- Depolarisation
- Repolarisation
- Hyperpolarisation
- Returns to resting potential
15
Q
What happens during depolarisation?
A
- Energy from a stimulus causes some Na+ v.g channels to open allowing some Na+ to get in
- If the threshold value is reached more Na+ channels open and an influx of sodium ions enter making the cell +30mV
16
Q
What happens during repolarisation?
A
- Once the action potential has been reached the Na+ v.g channels close and the K+ v.g channels open
- K+ start to leave the cell until an influx of K+ ions leave the cell
17
Q
What happens during hyperpolarisation?
A
- K+ keeps leaving the cell until the cell is more negative than the resting potential
- v.g K+ channels close allowing an electrochemical gradient to be re established
18
Q
What is the refractory period?
A
When no stimulus is large enough to raise membrane potential to threshold value
19
Q
What is the ‘all or nothing’ principle?
A
Any stimulus that causes the membrane to reach threshold potential will generate an action potential
20
Q
What is the role of myelin?
A
Increases speed at which action potentials can travel along the neurone
21
Q
Where do action potentials occur?
A
- Only at the nodes of Ranvier
- Depolarisation cannot occur at sections of the axon that are myelinated as it stops the diffusion of Na+ and K+ ions
22
Q
Where’s the synaptic cleft found?
A
Gap between 2 neurones
23
Q
What is the neurone before a synaptic cleft known as?
A
Pre-synaptic membrane/neurone
- Known as the synaptic knob
24
Q
What is the neurone after the synaptic cleft known as?
A
Post-synaptic membrane/neurone
25
How are nerve impulses passed across the synaptic cleft?
By the diffusion of chemicals known as neurotransmitters (e.g, acetylcholine)
26
How are neurotransmitters contained in the synaptic knob?
As vesicles
27
Describe the stages that allow an action potential to be transmitted across the synaptic cleft.
1. When an action potential arrives at the end of the axon of the presynaptic neurone the membrane becomes depolarised causing v.g calcium channels to open
2. Calcium ions diffuse into the synaptic knob causing vesicles to move towards the presynaptic membrane where they fuse with it and release chemical messengers via exocytosis
3. The neurotransmitters diffuse across the synaptic cleft and bind with receptor molecules on the postsynaptic membrane
4. This cause sodium channels to open on the postsynaptic membrane allowing sodium to diffuse into the cell
5. If enough neurotransmitters molecules bind with receptors than an action potential is generated
28
What determines if an action potential is generated at the presynaptic knob?
- Depends on whether or not threshold potential is reached which depends on the number of action potentials arriving at the presynaptic knob
- Many action potentials will cause more neurotransmitter to be released by exocytosis which will cause many sodium ion channels to open increasing the likelihood of threshold being reached
29
What are rod cells?
- Sensitive to light intensity so can detect the presence and brightness of light
- Images generated in black and white
- Connected to a single sensory neurone
- Evenly distributed
- Contains a pigment called rhodopsin
30
What are cone cells?
- Only see primary colours
- Only respond to high light intensities
- Connected to 3 sensory neurones
- Contains a pigment called iodopsin
31
What are photoreceptors?
Special cells in the eye's retina converts light energy into signals that are sent to the brain
32
What happens to rod cells in the light?
1. When light hits rhodopsin it breaks apart into retinal and opsin this is known as bleaching
2. Bleaching causes sodium ion channels to close preventing sodium ions from diffusing back into the cell
3. The sodium ions are still being actively transported out the cell till it becomes very negative until it reaches a hyperpolarised state
4. The hyperpolarised rod cell stops releasing an inhibitory neurotransmitter, so the generation of an action potential in the neighbouring bipolar neurone is no longer inhibited
33
What happens to rod cells in the dark?
1. Sodium ions are actively pumped out of rod cells generating a concentration gradient
2. Sodium ions then diffuse back into rod cells via sodium channels, the cell is now said to be depolarised
3. The depolarised rod cell releases neurotransmitters to the bipolar neurone, this neurotransmitter inhibits an action potential
34
What is the role of Auxins in plants?
Auxin is a growth factor that stimulates cell elongation in plant shoots and inhibits growth in cells in plant roots
35
What is the role of Giberellins in plants?
Stem elongation, flowering and seed germination
36
What is the role of Ethene in plants?
Fruit ripening
37
What is tropism?
A plant's growth response to an external stimulus
38
What is the difference between positive and negative tropism?
Positive tropism - growth towards stimulus
Negative tropism - growth away from stimulus
39
Is shoots and roots positively or negatively phototropic?
Shoots - positively phototropic as they grow towards light
Roots - negatively phototropic as they grow away from light
40
Is shoots and roots positively or negatively geotropic?
Shoots - negatively geotropic as they grow away upwards away from gravity
Roots - positively geotropic as they grow downwards towards gravity
41
What is the role of cytokinins in plants?
Stimulate cell division and cell differentiation
42
What is the role of IAA in plants?
- The redistribution of IAA is affected by environmental stimuli leading to an uneven distribution of IAA in different parts of the plant
- This brings about uneven plant growth
43
How does IAA affect plant growth in shoots?
- When light shines unevenly, IAA is transported to the shaded side
- This causes an accumulation of IAA on the shaded side causing cell elongation bending the shoot towards the light
(The concentration of IAA determines cell elongation so a higher conc increases cell elongation)
44
How does IAA affect plant growth in roots?
- IAA is transported towards the lower side of plant roots, the resulting high concentration of auxin at the lower side of the root inhibits cell elongation (in order to cause a positive geotropic response)
- As a result, the lower side grows at a slower rate than the upper side of the root, causing the root to bend downwards
45
What is saltatory conduction?
The process of an impulse jumping from node-to-node
